Menopause brings about profound physiological changes, including the acceleration of insulin resistance and other abnormalities, in which adipose tissue can play a significant role. This study analyzed the effect of ovariectomy and estradiol substitution on the metabolic parameters and transcriptomic profile of adipose tissue in prediabetic females of hereditary hypertriglyceridemic rats (HHTgs). The HHTgs underwent ovariectomy (OVX) or sham surgery (SHAM), and half of the OVX group received 17β-estradiol (OVX+E2) post-surgery. Ovariectomy resulted in weight gain, an impaired glucose tolerance, ectopic triglyceride (TG) deposition, and insulin resistance exemplified by impaired glycogenesis and lipogenesis. Estradiol alleviated some of the disorders associated with ovariectomy; in particular, it improved insulin sensitivity and reduced TG deposition. A transcriptomic analysis of perimetrial adipose tissue revealed 809 differentially expressed transcripts in the OVX vs. SHAM groups, mostly pertaining to the regulation of lipid and glucose metabolism, and oxidative stress. Estradiol substitution affected 1049 transcripts with overrepresentation in the signaling pathways of lipid metabolism. The principal component and hierarchical clustering analyses of transcriptome shifts corroborated the metabolic data, showing a closer resemblance between the OVX+E2 and SHAM groups compared to the OVX group. Changes in the adipose tissue transcriptome may contribute to metabolic abnormalities accompanying ovariectomy-induced menopause in HHTg females. Estradiol substitution may partially mitigate some of these disorders.

Physical activity is effective for preventing and treating type 2 diabetes, but some individuals do not achieve metabolic benefits from exercise (\"non-responders\"). We investigated non-responders in terms of insulin sensitivity changes following a 12-week supervised strength and endurance exercise program. We used a hyperinsulinaemic euglycaemic clamp to measure insulin sensitivity among 26 men aged 40-65, categorizing them into non-responders or responders based on their insulin sensitivity change scores. The exercise regimen included VO2max, muscle strength, whole-body MRI scans, muscle and fat biopsies, and serum samples. mRNA sequencing was performed on biopsies and Olink proteomics on serum samples. Non-responders showed more visceral and intramuscular fat and signs of dyslipidaemia and low-grade inflammation at baseline and did not improve in insulin sensitivity following exercise, although they showed gains in VO2max and muscle strength. Impaired IL6-JAK-STAT3 signalling in non-responders was suggested by serum proteomics analysis, and a baseline serum proteomic machine learning (ML) algorithm predicted insulin sensitivity responses with high accuracy, validated across two independent exercise cohorts. The ML model identified 30 serum proteins that could forecast exercise-induced insulin sensitivity changes.

Physical activity is integral to metabolic health, particularly in addressing insulin resistance and related disorders such as type 2 diabetes mellitus (T2DM). Studies consistently demonstrate a strong association between physical activity levels and insulin sensitivity. Regular exercise interventions were shown to significantly improve glycemic control, highlighting exercise as a recommended therapeutic strategy for reducing insulin resistance. Physical inactivity is closely linked to islet cell insufficiency, exacerbating insulin resistance through various pathways including ER stress, mitochondrial dysfunction, oxidative stress, and inflammation. Conversely, physical training and exercise preserve and restore islet function, enhancing peripheral insulin sensitivity. Exercise interventions stimulate β-cell proliferation through increased circulating levels of growth factors, further emphasizing its role in maintaining pancreatic health and glucose metabolism. Furthermore, sedentary lifestyles contribute to elevated oxidative stress levels and ceramide production, impairing insulin signaling and glucose metabolism. Regular exercise induces anti-inflammatory responses, enhances antioxidant defenses, and promotes mitochondrial function, thereby improving insulin sensitivity and metabolic efficiency. Encouraging individuals to adopt active lifestyles and engage in regular exercise is crucial for preventing and managing insulin resistance and related metabolic disorders, ultimately promoting overall health and well-being.

Rising rates of insulin resistance and an ageing population are set to exact an increasing toll on individuals and society. Here we examine the contribution of age and insulin resistance to the association of cerebral blood flow and glucose metabolism; both critical process in the supply of energy for the brain. Thirty-four younger (20-42 years) and 41 older (66-86 years) healthy adults underwent a simultaneous resting state MR/PET scan, including arterial spin labelling. Rates of cerebral blood flow and glucose metabolism were derived using a functional atlas of 100 brain regions. Older adults had lower cerebral blood flow than younger adults in 95 regions, reducing to 36 regions after controlling for cortical atrophy and blood pressure. Lower cerebral blood flow was also associated with worse working memory and slower reaction time in tasks requiring cognitive flexibility and response inhibition. Younger and older insulin sensitive adults showed small, negative correlations between relatively high rates of regional cerebral blood flow and glucose metabolism. This pattern was inverted in insulin resistant older adults, who showed hypoperfusion and hypometabolism across the cortex, and a positive correlation. In insulin resistant younger adults, the association showed inversion to positive correlations, although not to the extent seen in older adults. Our findings suggest that the normal course of ageing and insulin resistance alter the rates of and associations between cerebral blood flow and glucose metabolism. They underscore the criticality of insulin sensitivity to brain health across the adult lifespan.

BACKGROUND: Dietary fiber (DF) consumption was reported to improve insulin sensitivity, change the tryptophan metabolism, and alter the gut microbiota. Herein, this study aimed to investigate the effects of DF consumption on insulin sensitivity, tryptophan metabolism, and gut microbiota composition in sows during late pregnancy, and explore the relationship between tryptophan metabolites and insulin sensitivity regulated by DF supplementation.
RESULTS: Twelve sows were randomly assigned to two dietary treatment groups (six/group): the low-fiber (LF) group, which was fed a basal diet, and the high-fiber (HF) group, which was fed the basal diet supplemented with 22.60 g/kg inulin and 181.60 g/kg cellulose. During late pregnancy, meal test, glucose tolerance test, and insulin challenge test were used to investigate the insulin sensitivity of sows, using the percutaneous brachiocephalic vein catheterization technique. High DF consumption resulted in improved insulin sensitivity, especially during the second and third trimesters, and promoted serotonin production from tryptophan. Additionally, plasma serotonin concentration was positively correlated with the insulin sensitivity index during late pregnancy. Moreover, DF consumption elevated fecal short-chain fatty acid (SCFA) concentrations, altered fecal microbial diversity, and increased the abundances of Rikenellaceae_RC9_gut_group, Alloprevotella, Parabacteroides, Roseburia, and Sphaerochaeta, which were positively correlated to plasma serotonin concentration.
CONCLUSIONS: DF consumption improved insulin sensitivity during late pregnancy in sows, which improved microbial diversity in fecal samples and increased fecal SCFA concentrations, resulting in a positive correlation with plasma serotonin level.

Excessive iron accumulation in metabolic organs such as the adipose tissue, liver, and skeletal muscle is associated with increased diabetes risk. Tissue-resident macrophages serve multiple roles including managing inflammatory tone and regulating parachymal iron homeostasis; thus protecting against metabolic dysfunction upon iron overload. The scavenger receptor CD163 is uniquely present on tissue-resident macrophages, and plays a significant role in iron homeostasis by clearing extracellular hemoglobin-haptoglobin complexes, thereby limiting oxidative damage caused by free hemoglobin in metabolic tissues. We show that the absence of CD163 exacerbates glucose intolerance and insulin resistance in male mice with obesity. Additionally, loss of CD163 reduced the expression of iron regulatory genes (Tfr1, Cisd1, Slc40a1) in adipose tissue macrophages and anti-inflammatory (M2-like) bone marrow-derived macrophages (BMDMs). Further, CD163 deficiency mediated a pro-inflammatory shift and limited hemoglobin scavenging specifically in M2-like BMDMs. To this end, iron buffering was diminished in inguinal white adipose tissue (iWAT) macrophages in vivo, which culminated in iron spillover into adipocytes and CD45+CD11B- non-myeloid immune cells in iWAT. These findings show that CD163 on tissue-resident macrophages is critical for their anti-inflammatory and hemoglobin scavenging roles, and its absence results in impaired systemic insulin action in an obese setting.

Fructose is a commonly consumed monosaccharide implicated in developing several metabolic diseases. Previously, elevated branched-chain amino acids (BCAA) have been correlated with the severity of insulin resistance. Most recently, the effect of fructose consumption on the downregulation of BCAA catabolic enzymes was observed. Thus, this mechanistic study investigated the effects of physiologically attainable levels of fructose, both with and without concurrent insulin resistance, in a myotube model of skeletal muscle.
METHODS: C2C12 mouse myoblasts were treated with fructose at a concentration of 100 µM (which approximates physiologically attainable concentrations in peripheral circulation) both with and without hyperinsulinemic-mediated insulin resistance. Gene expression was assessed by qRT-PCR, and protein expression was assessed by Western blot. Oxygen consumption rate and extracellular acidification rate were used to assess mitochondrial oxidative and glycolytic metabolism, respectively. Liquid chromatography-mass spectrometry was utilized to analyze leucine, isoleucine and valine concentration values.
RESULTS: Fructose significantly reduced peak glycolytic and peak mitochondrial metabolism without altering related gene or protein expression. Similarly, no effect of fructose on BCAA catabolic enzymes was observed; however, fructose treatment resulted in elevated total extracellular BCAA in insulin-resistant cells.
CONCLUSIONS: Collectively, these observations demonstrate that fructose at physiologically attainable levels does not appear to alter insulin sensitivity or BCAA catabolic potential in cultured myotubes. However, fructose may depress peak cell metabolism and BCAA utilization during insulin resistance.

Genes regulating body fat are shared with high fidelity by mice and humans, indicating that mouse knockout (KO) phenotyping might identify valuable anti-obesity drug targets. Male Mrs2 magnesium transporter (Mrs2) KO mice were recently reported as thin when fed high-fat diet (HFD). They also exhibited increased energy expenditure (EE)/body weight and had beiged adipocytes that, along with isolated hepatocytes, demonstrated increased oxygen consumption suggesting increased EE drove the thin phenotype. Here we provide our data on these and additional assays in Mrs2 KO mice. We generated Mrs2 KO mice by homologous recombination. HFD-fed male and female Mrs2 KO mice had significantly less body fat, measured by QMR, than WT littermates. HFD-fed Mrs2 KO mice did not demonstrate increased EE by indirect calorimetry and could not maintain body temperature at 4°C, consistent with their decreased BAT stores but despite increased beige WAT. Instead, when provided a choice between HFD and low-fat diet (LFD), Mrs2 KO mice showed a significant 15% decrease in total energy intake resulting from significantly lower HFD intake that offset numerically increased LFD intake. Food restriction studies performed using WT mice suggested that this decrease in energy intake could explain the loss of body fat. OGTT studies revealed significantly improved insulin sensitivity in Mrs2 KO mice. We conclude that HFD-fed Mrs2 KO mice are thin with improved insulin sensitivity, and that this favorable metabolic phenotype is driven by hypophagia. Further evaluation is warranted to determine the suitability of MRS2 as a drug target for anti-obesity therapeutics.

OBJECTIVE: Is resting energy expenditure (REE) altered in women with polycystic ovary syndrome (PCOS)?
CONCLUSIONS: Women with PCOS have a reduction in REE, when corrected for fat-free mass, independent of PCOS clinical phenotypes and BMI categories.
BACKGROUND: Obesity is an important issue in women with PCOS, in terms of frequency and pathophysiological implications. It has been hypothesized that obesity may be favoured by alterations in REE, but the studies have been limited and conflicting.
METHODS: This case-control study was a comparison of 266 women with PCOS and 51 healthy controls, recruited in the Verona 3P study from 2010 to 2021.
METHODS: Women with PCOS diagnosed by the Rotterdam criteria, with normal thyroid function and no interfering medications, were referred to the outpatient clinic of a tertiary care centre of endocrinology and metabolism for a measurement of REE. Healthy controls were recruited in the same period and submitted to the same procedure. In all subjects, REE was measured by indirect calorimetry and serum androgens were measured by LC-MS/MS. In women with PCOS, insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp.
RESULTS: REE was similar in women with PCOS and controls. However, REE corrected for fat-free mass (REE/FFM) was significantly lower in women with PCOS than in controls (31.8 ± 4.0 vs 35.4 ± 3.9 kcal/kgFFM·day, P < 0.001). REE/FFM did not differ between normal-weight, overweight, or obese women with PCOS, and each of these subgroups showed lower REE/FFM values than controls. Reduced REE/FFM values were found in each phenotype of the syndrome. In multiple regression analysis, REE/FFM was independently associated with age and PCOS status, but not with fat mass. In PCOS women, REE/FFM was independently and directly associated with ovarian follicle number.
CONCLUSIONS: Limitations of the study are the cross-sectional design, which limits the causal inference of the results, and the unavailability of precise information about lifestyle factors, which may be potential confounders. Further prospective studies are needed to establish the importance of this phenomenon in contributing to the weight excess of PCOS.
CONCLUSIONS: A reduction of REE could potentially favour weight gain in women with PCOS and possibly contribute to the altered metabolic profile typical of this condition, even counteracting the therapeutic strategies aimed to reduce excess body fat in these women. Nevertheless, the presence of this abnormality in both obese/overweight and normal-weight patients suggests that other factors must play a role in this phenomenon.
BACKGROUND: This work was supported by academic grants to PM from the University of Verona (FUR 2010-2022). All authors declare no conflict of interest.
BACKGROUND: N/A.

Melatonin is a pineal hormone that modulates the circadian system and exerts soporific and phase-shifting effects. It is also involved in many other physiological processes, such as those implicated in cardiovascular, endocrine, immune, and metabolic functions. However, the role of melatonin in glucose metabolism remains contradictory, and its action on human adipose tissue (AT) explants has not been demonstrated. We aimed to assess whether melatonin (a pharmacological dose) influences insulin sensitivity in human AT. This will help better understand melatonin administration\'s effect on glucose metabolism. Abdominal AT (subcutaneous and visceral) biopsies were obtained from 19 participants with severe obesity (age: 42.84 ± 12.48 years; body mass index: 43.14 ± 8.26 kg/m2) who underwent a laparoscopic gastric bypass. AT biopsies were exposed to four different treatments: control (C), insulin alone (I) (10 nM), melatonin alone (M) (5000 pg/mL), and insulin plus melatonin combined (I + M). All four conditions were repeated in both subcutaneous and visceral AT, and all were performed in the morning at 8 a.m. (n = 19) and the evening at 8 p.m. (in a subsample of n = 12). We used western blot analysis to determine insulin signaling (using the pAKT/tAKT ratio). Furthermore, RNAseq analyses were performed to better understand the metabolic pathways involved in the effect of melatonin on insulin signaling. As expected, insulin treatment (I) increased the pAKT/tAKT ratio compared with control (p < .0001). Furthermore, the addition of melatonin (I + M) resulted in a decrease in insulin signaling as compared with insulin alone (I); this effect was significant only during the evening time (not in the morning time). Further, RNAseq analyses in visceral AT during the evening condition (at 8 p.m.) showed that melatonin resulted in a prompt transcriptome response (around 1 h after melatonin addition), particularly by downregulating the insulin signaling pathway. Our results show that melatonin reduces insulin sensitivity in human AT during the evening. These results may partly explain the previous studies showing a decrease in glucose tolerance after oral melatonin administration in the evening or when eating late when endogenous melatonin is present.